Tissue ablation systems and method

ABSTRACT

Tissue is treated using a radiofrequency power supply connected to an applicator having a chamber filled with an electrically non-conductive gas surrounded by a thin dielectric wall. A radiofrequency voltage is applied at a level sufficient to ionize the gas into a plasma and to capacitively couple the ionized plasma with the tissue to deliver radiofrequency current to ablate or otherwise treat the tissue.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 12/944,466 (Attorney Docket No. 37644-703.203, now U.S. Pat. No.______), filed Nov. 11, 2010, which is a non-provisional and claims thebenefit of Provisional Application No. 61/307,362 (Attorney Docket No.37644-703.103), filed on Feb. 23, 2010, and Provisional Application No.61/261,246 (Attorney Docket No. 37644-703.102), filed on Nov. 13, 2009,the full disclosures of which are incorporated herein by reference. Thisapplication is also related to Ser. No. 12/541,043 (Attorney Docket No.37644-703.201; now U.S. Pat. No. 8,372,068) filed on Aug. 13, 2009 andto Ser. No. 12/541,050 (Attorney Docket No. 37644-703.202; now U.S. Pat.No. 8,382,753) filed on Aug. 13, 2009, both of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electrosurgical devices and relatedmethods for rapid, controlled ablation of tissue. More particularly, thepresent invention relates to treating tissue with a radiofrequencycurrent delivered through an electrically non-conductive gas which isionized to capacitively couple to surrounding tissue through a thindielectric layer surrounding the gas.

The treatment of diseased organs, such as the uterus and thegallbladder, by ablation of an endometrial or mucosal layer surroundingthe interior of the organ has long been proposed. Such internal surfaceablation can be achieved by heating the surface, treating the surfacewith microwave energy, treating the surface with cryoablation, anddelivering radiofrequency energy to the surface. Of particular interestto the present invention, a variety of radiofrequency ablationstructures have been proposed including solid electrodes, balloonelectrodes, metalized fabric electrodes, and the like. While ofteneffective, at least most of the prior electrode designs have sufferedfrom one or more deficiencies, such as relatively slow treatment times,incomplete treatments, non-uniform ablation depths, and risk of injuryto adjacent organs.

For these reasons, it would be desirable to provide methods andapparatus for the radiofrequency ablation of internal tissue surfaceswhich are rapid, provide for uniform ablation depths, which assurecomplete ablation over the entire targeted surface, and which reduce therisk of injury to adjacent organs. At least some of these objectiveswill be met by the inventions described hereinbelow.

2. Description of the Background Art

U.S. Pat. No. 4,979,948, describes a balloon filled with an electrolytesolution for distributing radiofrequency current to a mucosal layer viacapacitive coupling. US 2008/097425, having common inventorship with thepresent application, describes delivering a pressurized flow of a liquidmedium which carries a radiofrequency current to tissue, where theliquid is ignited into a plasma as it passes through flow orifices. U.S.Pat. No. 5,891,134 describes a radiofrequency heater within an enclosedballoon. U.S. Pat. No. 6,041,260 describes radiofrequency electrodesdistributed over the exterior surface of a balloon which is inflated ina body cavity to be treated. U.S. Pat. No. 7,371,231 and US 2009/054892describe a conductive balloon having an exterior surface which acts asan electrode for performing endometrial ablation. U.S. Pat. No.5,191,883 describes bipolar heating of a medium within a balloon forthermal ablation. U.S. Pat. No. 6,736,811 and U.S. Pat. No. 5,925,038show an inflatable conductive electrode.

BRIEF SUMMARY OF THE INVENTION

The present invention provides methods, apparatus, and systems fortreating tissue of a patient. The treatment generally comprisesdelivering a radiofrequency current to the tissue in order to heat andusually ablate the tissue to a desired depth. Current is delivered tothe tissue from a radiofrequency energy source through a firstdielectric medium and a second dielectric medium in series with thefirst medium. The first dielectric medium will usually comprise anelectrically non-conductive gas which may be ionized to form a plasma,typically by application of a high voltage radiofrequency voltage, butoptionally by the direct application of heat to the gas, furtheroptionally by the application of both the high radiofrequency voltageand heat to the gas. The second dielectric medium will separate thefirst medium from the target tissue, typically comprising a thindielectric material, such as silicone or a silicone-based material, moretypically comprising a thin dielectric wall which defines an interiorchamber which contains the electrically non-conductive gas. Theradiofrequency current is thus delivered to the tissue by applying aradiofrequency voltage across the first and second dielectric media sothat the first dielectric becomes ionized, typically forming a gasplasma, and the second dielectric allows current flow to the tissue viacapacitive coupling.

Methods for treating tissue of a patient in accordance with the presentinvention comprise containing an electrically non-conductive gas in aninterior chamber of an applicator having a thin dielectric wallsurrounding at least a portion of the interior chamber. An externalsurface of the thin dielectric wall is engaged against a target regionof the tissue, and a radiofrequency voltage is applied across the gasand thin wall, where the voltage is sufficient to ionize the gas toinitiate a plasma in the gas and to capacitively couple the current inthe gas plasma across the dielectric wall and into the engaged tissue.

The electrically non-conductive gas may be held statically within thechamber, but will more often be actively flowing through the chamber ofthe applicator. The flow rate of the non-conductive gas will typicallybe in the range from about 1 ml/sec to 50 ml/sec, preferably from 10ml/sec to 30 ml/sec. The interior chamber will have a volume in therange from 0.01 ml to 100 ml, typically from 2 ml to 10 ml. Usually, theelectrically non-conductive gas will be argon or another noble gas ormixture of noble gases.

The dielectric wall of the applicator may assume a variety ofconfigurations. In a first embodiment, the dielectric wall will have agenerally fixed shape that will remain constant regardless of theinternal pressurization of the contained gas. Alternatively, thedielectric wall may be elastic, conformable, slack, or otherwise havinga changeable shape which can conform to the engaged tissue surface. Insome examples, the thin dielectric wall will comprise a balloon or otherinflatable structure which is expanded by increasing an internalpressure of the electrically non-conductive gas or other medium.Alternatively, a separate frame, cage, spring, or other mechanicaldeployment structure could be provided within an elastic or non-elasticconformable thin dielectric wall. In the latter case, the frame or otherstructure can be configured and reconfigured to shape the thindielectric wall as desired in the method.

The voltage is applied to the tissue by providing a first electrodesurface coupled to the non-conductive gas and a second electrode surfacecoupled to the patient tissue. A radiofrequency voltage is then appliedacross the first and second electrodes in order to both ionize theelectrically non-conductive gas (forming a plasma) within the interiorchamber and to capacitively couple the charged plasma with tissue acrossthe thin dielectric wall.

The voltage applied to the first and second dielectric media will dependon the distance between the first electrode surface and the dielectricwall as well as the resistance between the dielectric wall and thesecond electrode which is in contact with the tissue, typically being inthe range between 500V (rms) and 2500V (rms). In the exemplaryembodiments, the first electrode surface will usually be in or on theinterior chamber or a gas flow path leading to the interior chamber, andthe second electrode surface will be in contact with the patient'stissue, often being disposed on a shaft or other external surface of thetreatment device.

In a second aspect of the present invention, apparatus for deliveringradiofrequency current to tissue comprises a body having a support end,a working end, and an interior chamber. A thin dielectric wall surroundsat least a portion of the interior chamber and has an external surfacedisposed at the working end of the body. A gas inlet will be provided toconnect to the chamber for delivery of an electrically non-conductivegas, either in a continuously flowing mode or in a static mode. A firstelectrode structure is provided which has a surface exposed to eitherthe interior chamber or the gas inlet. A second electrode structure isalso provided and has a surface adapted to contact tissue, typicallybeing somewhere on the body, more typically being on a handle or shaftportion of the device. The apparatus further includes a radiofrequencypower supply connected to apply a radiofrequency voltage across thefirst and second electrode structures, wherein the voltage is sufficientto initiate ionization of the gas into a plasma within the chamber. Thevoltage will further be sufficient to capacitively couple the current inthe plasma across the dielectric wall and into tissue adjacent theexternal surface.

The specific structure of the body may vary. In a first example, thedielectric wall may comprise a rigid material, typically selected fromthe group consisting of a ceramic, glass, and polymer. The rigidmaterial may be formed into a variety of geometries, including a tube,sphere, or the like. Usually, the dielectric wall will have a thicknessin the range from about 0.002 in to 0.1 in, usually from 0.005 in to0.05 in.

In alternative embodiments, the dielectric wall may comprise aconformable material, typically a silicone. Such conformable dielectricwalls will typically have a thickness in the range from about 0.004 into 0.03 in, usually from 0.008 in to 0.015 in. The conformable wall maybe non-distensible or may be elastic so that the wall structure may beinflated. For either non-distensible or elastic dielectric walls, thedevice may further comprise a frame which supports the conformablematerial, usually where the frame can be expanded and contracted to openand close the dielectric wall.

The apparatus of the present invention will typically also include ashaft or other handle structure connected to the support end of thebody. Usually, the shaft will have a lumen which extends into the gasinlet of the body to deliver the electrically non-conductive gas to thechamber. The shaft or handle may also include at least a second lumenfor removing the electrically non-conductive gas from the chamber sothat the gas may be recirculated in a continuous flow. Often, the firstelectrode will be at least partly in the first lumen of the device,although it may also be within the chamber or within both the firstlumen and the chamber. The second electrode will usually be disposed atleast partly over an exterior surface of the device, typically over theshaft, although in certain systems the second electrode could bedisposed on a separate dispersal pod.

Apparatus according to the present invention will have an interiorchamber volume in the range from 0.01 ml to 20 ml, typically from 1 mlto 10 ml. The dielectric wall will have an area in the range from 1 mm²to 100 mm², typically from 5 mm² to 50 mm². The first electrode surfacewill have an area in contact with the electrically non-conductive gas inthe range from 0.01 mm² to 10 mm², typically from 1 mm² to 5 mm².Additionally, the second electrode structure will have an area availableto contact tissue in the range from 0.5 mm² to 50 mm², usually from 1mm² to 10 mm².

The radiofrequency power supply may be of general construction as oftenused in electrosurgery. The power supply will typically be configured todeliver a voltage in the range from 500 V (rms) to 2500 V (rms), usuallyfrom 600 V (rms) to 1200V (rms), typically at a current in the rangefrom 0.1 A to 1 A, typically from 0.2 A to 0.5 A, and at a frequency inthe range from 450 kHz to 550 MHz, usually from 480 kHz to 500 MHz.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the invention and to see how it may becarried out in practice, some preferred embodiments are next described,by way of non-limiting examples only, with reference to the accompanyingdrawings, in which like reference characters denote correspondingfeatures consistently throughout similar embodiments in the attacheddrawings.

FIG. 1 is a schematic view of an ablation system corresponding to theinvention, including an electrosurgical ablation probe, RF power sourceand controller.

FIG. 2A is a view of the ablation probe of FIG. 1 configured with asharp tip for ablation of a tumor.

FIG. 2B is another view of the probe of FIG. 2A after being penetratedinto the tumor.

FIG. 3 is an enlarged schematic view of the working end of the probe ofFIG. 1 that provides a gas electrode within an interior of a thin-walldielectric structure.

FIG. 4A is a sectional view of an alternative thin-wall cylindricaldielectric structure in which support elements are formed within thedielectric structure.

FIG. 4B is a sectional view of a portion of another thin-wall planardielectric structure in which support elements are in a waffle-likeconfiguration.

FIG. 5A is a sectional view of a portion of another thin-wall planardielectric structure in which support elements comprise post-likeelements.

FIG. 5B is a sectional view of a probe working end in which a thin-walldielectric structure with post-like support elements are provided aroundcore electrode.

FIG. 6 is a block diagram of components of one an electrosurgical systemcorresponding to the invention.

FIG. 7 is a block diagram of gas flow components of an electrosurgicalsystem corresponding to the invention.

FIG. 8 is a cut-away schematic view of a working end as in FIG. 3illustrating a step in a method of the invention wherein current iscoupled to tissue via a spark gap (or gas electrode) and capacitivecoupling through a thin-wall dielectric structure.

FIG. 9A is an enlarged schematic view of an aspect of the method of FIG.3 illustrating the step positioning an ionized gas electrode andthin-wall dielectric in contact with tissue.

FIG. 9B is a schematic view of a subsequent step of applying RF energyto create an arc across a gas and capacitive coupling through thethin-wall dielectric to cause current flow in a discrete path in tissue.

FIG. 9C is a schematic view similar to FIG. 9B depicting the scanning ofcurrent flow to another random path in the tissue.

FIG. 9D is a schematic view similar to FIGS. 9A-9C depicting the thermaldiffusion from the plurality of scanned current flows in the tissue.

FIG. 10 is a circuit diagram showing the electrical aspects andcomponents of the energy delivery modality.

FIG. 11A is a sectional view of the working end of FIG. 3 positioned intissue illustrating a step in a method of using the working end whereincurrent is coupled to tissue via an ionized gas and capacitive couplingthrough a thin wall dielectric structure.

FIG. 11B is a sectional view similar to that of FIG. 11A illustratinganother step in the method in which the ablated tissue volume is shown.

FIG. 12 is a sectional view of an alternate working end similar to thatof FIG. 3 in a method of use, the dielectric structure having a centralsupport member functioning as (i) an electrode and as (ii) a gas flowdirecting means.

FIG. 13 is a block diagram of one method corresponding to the invention.

FIG. 14 is a block diagram of another method corresponding to theinvention.

FIG. 15 is a block diagram of another method corresponding to theinvention.

FIG. 16 is a block diagram of another method corresponding to theinvention.

FIG. 17 is a block diagram of another method corresponding to theinvention.

FIG. 18A is plan view of an alternate ablation probe that carries aplurality of extendable needle-like ablation elements from a sheath,each element having a dielectric structure with varied dielectricparameters for directional control of capacitive coupling and thusdirectional control of ablation.

FIG. 18B is another view of the ablation probe of FIG. 18A with theplurality of extendable needle ablation elements extended from thesheath.

FIG. 19 is an enlarged view of a working end of the ablation probe ofFIGS. 18A-18B with a tissue volume targeted for ablation and resection.

FIG. 20 is a sectional view of ablated tissue using the working end ofFIG. 19 showing the directed capacitive coupling and directed ablation.

FIG. 21 is a schematic view of a tumor ablation method using a pluralityof working ends similar to that of FIGS. 19-20 for directed capacitivecoupling and directed ablation.

FIG. 22 is a sectional view of an alternate working end similar to thatof FIGS. 3 and 12 with a non-uniform thickness dielectric structure fordirectional control of capacitive coupling and thus directional controlof ablation.

FIG. 23 is a sectional view of a non-uniform thickness dielectricstructure for directional control of capacitive coupling to tissue.

FIG. 24 is a sectional view of a uniform thickness dielectric structurewith different materials for directional control of capacitive couplingto tissue.

FIG. 25A is a sectional view of a working end of an ablation probesimilar to that of FIG. 12 with an expandable thin-wall dielectricstructure in a non-extended condition.

FIG. 25B is a sectional view of the working end of FIG. 25A with theexpandable thin-wall dielectric structure in an extended condition insoft tissue, the structure configure for expansion by gas inflationpressure.

FIG. 25C is another sectional view as in FIG. 25B showing the capacitivecoupling of energy to the tissue from a contained plasma in theexpandable dielectric structure.

FIG. 25D is another sectional view as in FIG. 25B showing the region ofablated tissue after energy delivery.

FIG. 26 is another cross-sectional view of the expandable dielectricstructure in a non-extended condition folded within a translatablesheath.

FIG. 27 is a cut-away schematic view of a heart and a working end ofanother ablation probe similar to that of FIG. 25A with an expandablethin-wall dielectric structure configured for ablating about a pulmonaryvein to treat atrial fibrillation, with the structure configure forexpansion by gas inflation pressure.

FIG. 28 is an enlarged sectional schematic view of the working end ofFIG. 27 ablating a pulmonary vein.

FIG. 29 is a cut-away schematic view of a heart and deflectable workingend of another ablation probe configured for ablating a linear lesion totreat atrial fibrillation.

FIG. 30 is a schematic perspective view of the deflectable working endof FIG. 29 illustrating an elongate dielectric structure.

FIG. 31 is a cross-sectional view of the deflectable working end anddielectric structure of FIG. 30 illustrating an interior electrode.

FIG. 32 is a perspective view of another deflectable working end similarto that of FIGS. 30-31 for creating a circumferential lesion to treatatrial fibrillation.

FIG. 33 is a cut-away schematic view of a esophagus and working end ofanother ablation probe similar to that of FIG. 27 with an expandablethin-wall dielectric structure configured for expansion by an interiorskeletal framework.

FIG. 34 is a cut-away view of the expandable thin-wall dielectricstructure of FIG. 33 showing the interior skeletal support frame thatoptionally functions as an electrode.

FIG. 35 is a cut-away view of another expandable dielectric structuresimilar to FIG. 34 showing an alternative interior skeletal supportframe.

FIG. 36 is a sectional schematic view of a working end of anotherablation probe comprising first and second opposing jaws engaging tissuewith each jaw engagement surface including a thin-wall dielectricstructure, the jaws configured for sealing or coagulating tissue clampedtherebetween.

FIG. 37 is a schematic view of the working end of another embodimentwith an expandable thin dielectric walled structure with a plurality ofplasma-carrying chambers for performing another form of bi-polarablation.

FIG. 38 is a transverse sectional schematic view of the working end ofFIG. 30 taken along line 38-38 of FIG. 37 rotated 90° showing thecurrent flow in tissue.

FIG. 39 is a cut-away view of an alternative working end with athin-wall dielectric construct enclosing an interior chamber.

FIGS. 40A-40B are schematic views of the dielectric surface of FIG. 29showing the charge distribution on low charge mobility surfaces thatpermits dielectric barrier discharges to form a substantially stablepattern.

FIGS. 41A-41E are enlarged schematic views of the dielectric surface ofFIGS. 40A-40B illustrating the method of creating momentary lines ofelectrostatic flux to controllably couple RF energy to tissue.

FIG. 42 is a greatly enlarged cut-away schematic view of a portion of aworking end of FIG. 39 illustrating spatiotemporal switching oftransitory plasma streamers and further illustrating the method of Jouleheating of tissue.

FIG. 43 is a greatly enlarged cut-away view of a portion of a workingend FIG. 34 illustrating spatiotemporal switching of plasma streamersand further illustrating the method of heating the wall to thereafterconduct heat to tissue.

FIG. 44 is a block diagram of one method corresponding to the invention.

FIG. 45 is a block diagram of another method corresponding to theinvention.

FIG. 46 is a block diagram of another method corresponding to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Several embodiments of ablation systems useful for practicing ablationmethods corresponding to the present invention are shown in thedrawings. In general, each of these embodiments utilizes a neutral gascontained within a chamber that is at least partly enclosed by thin-walldielectric enclosure, wherein the dielectric wall provides forcapacitive coupling of RF current from the gas to through the dielectricto contacted tissue. A second electrode is in contact the tissue at anexterior of the dielectric enclosure. The system embodiments typicallyinclude an instrument with a working end including the thin-walldielectric enclosure for containing an ionizable gas. Current flow tothe tissue initiates when sufficient voltage is applied to ionize thecontained gas into a plasma and the contemporaneous capacitive couplingthrough the surrounding dielectric structure occurs. The invention thusprovides a voltage-based electrosurgical effect that is capable ofablating tissue to a controlled depth of 1 mm to 5 mm or more veryrapidly, wherein the depth of ablation is very uniform about the entiresurface of the dielectric enclosure. The instrument working end anddielectric enclosure can take a variety of forms, including but notlimited to an elongated shaft portion of a needle ablation device, adielectric expandable structure, an articulating member, a deflectablemember, or at least one engagement surface of an electrosurgical jawstructure. The system embodiments and methods can be used forinterstitial tissue ablation, intraluminal tissue ablation or topicaltissue ablation.

The system embodiments described herein utilize a thin-wall dielectricstructure or wall at an instrument working end that contains anelectrically non-conductive gas as a dielectric. The thin-walldielectric structure can be a polymer, ceramic or glass with a surfaceconfigured for contacting tissue. In one embodiment, an interior chamberwithin the interior of the thin-wall dielectric structure carries acirculating neutral gas or static neutral gas such as argon. An RF powersource provides current that is coupled to the neutral gas flow orstatic gas volume by an electrode disposed within the interior of theworking end. The gas flow or static gas contained within the dielectricenclosure is of the type that is non-conductive until it has beentransformed to a conductive plasma by voltage breakdown. The thresholdvoltage for breakdown of the gas will vary with variations in severalparameters, including the gas pressure, the gas flow rate, the type ofgas, and the distance from the interior electrode across the interiorchamber to the dielectric structure. As will be seen in some of theembodiments, the voltage and other operational parameters can bemodulated during operation by feedback mechanisms.

The gas, which is ionized by contact with a conductive electrode in theinstrument working end, functions as a switching mechanism that onlypermits current flow into targeted tissue when the voltage across thecombination of the gas, the dielectric structure and the contactedtissue reaches a predetermined threshold potential that causescapacitive coupling across the dielectric structure. By this means ofpermitting current flow only at a high threshold voltage thatcapacitively couples current to the tissue, the invention allows asubstantially uniform tissue effect within all tissue in contact withthe dielectric structure. Further, the invention allows the ionized gasto be created contemporaneously with energy application to tissue by theconversion of a non-conductive gas to a plasma.

In one embodiment of the apparatus, the ionized gas functions as anelectrode and comprises a gas flow that can conduct current across aninternal contained volume of the gas within a dielectric structure,typically from an electrode at an interior of a working end in contactwith the gas flow. The gas flow is configured for the purpose ofcoupling energy to the dielectric structure uniformly across the surfaceof the dielectric structure, but that will only conduct such energy whenthe non-conductive gas media has been transformed to a conductive plasmaby having been raised to a threshold voltage.

Definitions

Plasma. In general, this disclosure may use the terms “plasma” and“ionized gas” interchangeably. A plasma consists of a state of matter inwhich electrons in a neutral gas are stripped or “ionized” from theirmolecules or atoms. Such plasmas can be formed by application of anelectric field or by high temperatures. In a neutral gas, electricalconductivity is non-existent or very low. Neutral gases act as adielectric or insulator until the electric field reaches a breakdownvalue, freeing the electrons from the atoms in an avalanche process thusforming a plasma. Such a plasma provides mobile electrons and positiveions, an acts as a conductor which supports electric currents and canform spark or arc. Due to their lower mass, the electrons in a plasmaaccelerate more quickly in response to an electric field than theheavier positive ions, and hence carry the bulk of the current. Avariety of terms are known in the literature to describe a transientplasma discharge across a gas such as plasma filament, plasma streamer,plasma microstreamer, plasma wire or plasma hair. In this disclosure,the terms plasma filament and plasma streamer are used interchangeablyherein to describe visible plasma discharges within and across a gasvolume. A plasma filament may also be called a dielectric barrierdischarge herein when describing a plasma filament generated adjacentto, and as a function of, high voltage current coupling through adielectric wall.

Dielectric and dielectric loss. The term dielectric is used in itsordinary sense meaning a material that resists the flow of electriccurrent, that is, a non-conducting substance. An important property of adielectric is its ability to support an electrostatic field whiledissipating minimal energy in the form of heat. The lower the dielectricloss (the proportion of energy lost as heat), the more effective is adielectric material.

Dielectric constant or relative permittivity. The dielectric constant(k) or relative static permittivity of a material under given conditionsis a measure of the extent to which it concentrates electrostatic linesof flux, or stated alternatively is a number relating the ability of thematerial to carry alternating current to the ability of vacuum to carryalternating current. The capacitance created by the presence of amaterial is directly related to its dielectric constant. In general, amaterial or media having a high dielectric constant breaks down moreeasily when subjected to an intense electric field than do materialswith low dielectric constants. For example, air or another neutral gascan have a low dielectric constant and when it undergoes dielectricbreakdown, a condition in which the dielectric begins to conductcurrent, the breakdown is not permanent. When the excessive electricfield is removed, the gas returns to its normal dielectric state.

Dielectric breakdown. The phenomenon called dielectric breakdown occurswhen an electrostatic field applied to a material reaches a criticalthreshold and is sufficiently intense so that the material will suddenlyconduct current. In a gas or liquid dielectric medium, this conditionreverses itself if the voltage decreases below the critical point. Insolid dielectrics, such a dielectric breakdown also can occur and coupleenergy through the material. As used herein, the term dielectricbreakdown media refers to both solid and gas dielectrics that allowcurrent flow across the media at a critical voltage.

Degree of ionization. Degree of ionization describes a plasma'sproportion of atoms which have lost (or gained) electrons, and iscontrolled mostly by temperature. For example, it is possible for anelectrical current to create a degree of ionization ranging from lessthan 0.001% to more than 50.0%. Even a partially ionized gas in which aslittle as 0.1% or 1.0% of the particles are ionized can have thecharacteristics of a plasma, that is, it can strongly respond tomagnetic fields and can be highly electrically conductive. For thepurposes of this disclosure, a gas may begin to behave like conductiveplasma when the degree of ionization reaches approximately 0.1%, 0.5% or1.0%. The temperature of a plasma volume also relates to the degree ofionization. In particular, plasma ionization can be determined by theelectron temperature relative to the ionization energy. A plasma issometimes referred to as being “hot” if it is nearly fully ionized, or“cold” or a “technological plasma” if only a small fraction (forexample, less than 5% or less than 1%) of the gas molecules are ionized.Even in such a cold plasma, the electron temperature can still beseveral thousand degrees Celsius. In the systems according to thepresent invention, the plasmas are cold in this sense because thepercentage of ionized molecules is very low. Another phrase used hereinto describe a “cold” plasma is “average mass temperature” of the plasmawhich relates to the degree of ionization versus non-ionized gas andwhich averages the temperatures of the two gas volume components. Forexample, if 1% of a gas volume is ionized with an electron temperatureof 10,000° C., and the remaining 99% has a temperature of 150° C., thenthe mass average temperature will be 149.5° C. It has been found thatmeasuring the plasma temperature can be used to determine an approximatedegree of ionization which can be used for feedback control of appliedpower, and as a safety mechanism for preventing unwanted hightemperatures within a thin-wall dielectric structure.

Referring to FIG. 1, a first embodiment of a tissue ablation system 100utilizing principles of the present invention is shown. The system 100includes a probe 110 having a proximal handle 112 and an elongated shaftor extension member 114 that extends along axis 115. The handle 110 isfabricated of an electrically insulative material such as a plastic,ceramic, glass or combination thereof. The extension member 114 has aproximal end 116 coupled to handle 112. The extension member 114 extendsto a distal working end 120 that includes a dielectric member orstructure 122 that is configured for contacting tissue that is targetedfor ablation.

In the embodiment of FIG. 1, the working end 120 and dielectricstructure 122 is elongated and cylindrical with a cross-section rangingfrom about 0.5 mm to 5 mm or more with a length ranging from about 1 mmto 50 mm. The cross-section of the working end 120 can be round, oval,polygonal, rectangular or any other cross-section. As can be seen inFIGS. 2A-2B, in one embodiment, the working end 120 has a sharp tip 124for penetrating tissue to perform an ablation procedure, such asablating a tumor indicated at 125 in a tissue volume 130. In otherembodiment, the distal tip of a working end 120 can be blunt. In yetother embodiment, the entire working end can have a guide channeltherein for advancing the working end over a guide wire.

Now turning to FIG. 3, an enlarged view of the working end 120 of FIGS.1, 2A and 2B is shown. It can be seen that the dielectric structure 122has a thin wall 132 that provides an enclosure about an interior chamber135 that contains a gas media indicated at 140 in FIG. 3. In oneembodiment, the dielectric structure 122 can comprise a ceramic (e.g.,alumina) that has a a dielectric constant ranging from about 3 to 4. Thethickness of wall 132 can range from 0.002″ to 0.10″ depending on thediameter, or more typically 0.005″ to 0.050″ in a diameter ranging from1 to 4 mm. In other embodiment shown in FIG. 4A, the dielectricstructure 122 can comprise a ceramic, glass or polymer in a molded formwith strengthening support portions 142 or ribs that end axially,radially, helically or a combination thereof. The support portions 142alternatively can comprise members that are independent of a thin-wall132 of a dielectric material. In such an embodiment (FIG. 4A) as will bedescribed below, the thin wall portions 144 of the dielectric structure122 permit capacitive coupling of current to tissue while the supportportions 142 provide structural strength for the thin-wall portions 144.In another embodiment, a portion of which is shown in FIG. 4B, thedielectric structure 122 has support portions 142 in a waffle-likeconfiguration wherein thin-wall portions 144 are supported by thickerwall support portions 142. The waffle-like structure can besubstantially planar, cylindrical or have any other suitableconfiguration for containing a gas dielectric in a chamber indicated at135 on one side of the dielectric structure 122. In another embodimentof FIGS. 5A and 5B, the dielectric structure 122 can have supportportions 142 comprising posts that support the thin-wall portions 144over another supporting member 145. The planar dielectric structure 122can be used, for example, in planar jaw members for applying RF energyto seal tissue. In another example, FIG. 5B shows a blunt-tipped,cylindrical thin wall 132 of a dielectric structure 122 supported by acore supporting member 145. In the embodiment of FIG. 5B, the interiorchamber 135 which can contain a plasma comprises a space between thethin wall portions 144 and the core support member 145.

Referring again to FIG. 3, the extension member 114 is fabricated of anelectrically non-conductive material such as polymer, ceramic, glass ora metal with an insulative coating. The dielectric structure 122 can bebonded to extension member 114 by glues, adhesives or the like toprovide a sealed, fluid-tight interior chamber 135. In one embodiment, agas source 150 can comprise one or more compressed gas cartridges (FIGS.1 and 6). As will be described below (FIG. 6), the gas source is coupledto a microcontroller 155 that includes a gas circulation subcontroller155A which controls a pressure regulator 158 and also controls anoptional negative pressure source 160 adapted for assisting incirculation of the gas. The RF and controller box 162 in FIG. 1 caninclude a display 164 and input controls 165 for setting and controllingoperational parameters such as treatment time intervals, gas flows,power levels etc. Suitable gases for use in the system include argon,other noble gases and mixtures thereof.

Referring to FIG. 3, the gas source 150 provides a flow of gas media 140though a flexible conduit 166 to a first flow channel 170 in extensionmember 114 that communicates with at least one inflow port 172interfacing with interior chamber 135. The interior chamber 135 alsointerfaces with an outflow port 174 and second flow channel 180 inextension member 114 to thereby allow a circulating flow of gas media140 within the interior of dielectric structure 122.

Still referring to FIG. 3, a first polarity electrode 185 is disposedabout flow channel 170 proximate to the inflow port 172 thus being incontact with a flow of gas media 140. It should be appreciated thatelectrode 185 can be positioned in any more proximal location in channel170 in contact with the gas flow, or the electrode 185 can be withininterior chamber 135 of dielectric structure 122. The electrode 185 iselectrically coupled to a conductor or lead 187 that extends through theextension member and handle 112 and is coupled to a first pole of a highfrequency RF generator 200 which is controlled by controller 155 and RFsubcontroller 155B. An opposing polarity electrode 205 is disposed onthe exterior surface of extension member 114 and is electrically coupledby lead 207 to a second pole of RF generator 200.

The box diagrams of FIGS. 6 and 7 schematically depict the system,subsystems and components of one embodiment that is configured fordelivering ablative electrosurgical energy to tissue. In the box diagramof FIG. 6, it can be seen that an RF power source 200 and circuit iscontrolled by RF subcontroller 155B. Feedback control subsystems(described below) based on systems and probe pressure feedback, probetemperature feedback, and/or gas flow rate feedback are also operativelycoupled to controller 155. The system can be actuated by footswitch 208or another suitable switch. FIG. 7 shows a schematic of the flow controlcomponents relating to the flow of gas media through the system andprobe 110. It can be seen that a pressurized gas source 150 in linked toa downstream pressure regulator 158, an inflow proportional valve 210,flow meter 212 and normally closed solenoid valve 220. The valve 220 isactuated by the system operator which then allows a flow of gas media140 to circulate through flexible conduit 166 and probe 110. The gasoutflow side of the system includes a normally open solenoid valve 225,outflow proportional valve 226 and flowmeter 228 that communicate withnegative pressure source 160. The exhaust of the gas can be into theenvironment or into a containment system. A temperature sensor 230(e.g., thermocouple) is shown in FIG. 7 for monitoring the temperatureof outflow gases.

FIGS. 8 and 9A-9D schematically illustrate a method of the inventionwherein (i) the dielectric structure 122 and (ii) the contained neutralgas volume 140 function contemporaneously to provide first and seconddielectric media that cooperatively function as independent mechanismsto couple high voltage current to tissue in contact with the thin-walldielectric 132. The two dielectric components can be characterized ashaving complementary voltage thresholds levels at which only highvoltage current can couple through a plasma filament or streamer 235 inplasma 240 within chamber 135 and capacitively couple through thethin-wall dielectric 132 to allow a current to further pass through aleast resistive path 245 in the engaged tissue. In FIG. 8, the engagedtissue is assumed to be surrounding the dielectric structure 122 and istransparent. In the embodiment of FIG. 8, the electrode 185 is tubularand functions and a gas delivery sleeve wherein a neutral gas 140 canexit ports 250 in chamber 135. The high voltage current paths 245 inplasma filaments scan or move across and about the inner surface 248 ofthe dielectric structure 122 and within paths in the contacted tissuewhich can deliver a voltage-maximized current causing Joule heating inthe tissue. FIG. 8 provides a schematic view of what is meant by theterminology or plasma filament “scanning” the interior surface of thedielectric 132 wherein high intensity electrical fields are produced ininterior chamber 135 of dielectric structure 122 by capacitive couplingthrough the dielectric wall 132 until a voltage threshold is reached inthe neutral gas media 140 to convert the gas into a plasma 240 (see FIG.8) which in turn allows plasma filaments 235 to form within the chamber135 which randomly move or scan about the interior surface 248 of thedielectric wall. In one embodiment, movement or scanning of such plasmafilaments 235 within the chamber 135 (from electrode 185 to innersurface 248 of dielectric wall 132) is spatiotemporally chaotic and thedischarge occurs where there is a transient, reversible voltagebreakdown in a localized portion 252 of the dielectric wall 132, whichis determined by a transient highest conduction path 240 in engagedtissue to the second polarity electrode 205 (FIG. 3). An instant afterthe flow of current through the plasma 240 and path 245 in tissue, thelocalized portion 252 dissipates the electrical field and anothercapacitive coupling occurs through another plasma filament 235′ andcurrent path 245′ in tissue to cause electrosurgical ablation in anotherrandom, discrete location. In another embodiment, the plasma filamentscan be very fine resulting in the appearance of a glow discharge withinchamber 135 instead of spaces apart discrete plasma filaments.

FIGS. 9A-9D are enlarged schematic illustrations of the electrosurgicalablation method of FIG. 8 that depict other aspects of the ablationmethod. In FIG. 9A, it can be seen that the system and method isgeneralized to show clearly the first and second dielectric currenttransmission mechanisms characterized by selected voltage parameters tocause an electron avalanche in the gas and capacitive coupling in thethin-wall enclosure to optimize and maximize a form of high voltagecurrent delivery to an exemplary tissue 260. As described previously,the voltage threshold or dielectric breakdown mechanisms occur within(i) the gas dielectric or neutral gas volume 140 that is containedwithin an interior chamber 135 of dielectric structure 122 and (ii) thenon-gas dielectric or structure 122 shown as a plane in FIGS. 9A-9D.

FIG. 9A illustrates the working end components and tissue 260 prior tothe actuation and delivery of energy to the tissue. It can be seen thatthe gas media 140 is neutral and not yet ionized. The first polarityelectrode 185 positioned in the interior chamber 135 in contact withneutral gas 140 is shown schematically. The second polarity electrode205 in contact with tissue is also shown schematically, but theillustration represents another aspect of the invention in that thesecond electrode 205 can have a small surface area compared to thesurface areas of return electrodes/ground pads as in conventionalelectrosurgical systems. It has been found that the capacitively coupledenergy delivery mechanism of the invention does not cause tissue heatingat or about the surface of the second polarity electrode 205 as would beexpected in a conventional electrosurgical device. As will be describedbelow, it is believed that the constant flux in voltagebreakdown-initiated and capacitive coupling-initiated current paths inthe tissue 260 greatly reduces heat built up at or about the returnelectrode 205.

FIG. 9B illustrates the working end components and tissue 260 at aninstant in time immediately after the operator actuates the system anddelivers power to the probe working end. Several aspects of thevoltage-initiated breakdown ablation method are represented in FIG. 9B,including (i) in one aspect of the instant in time, the neutral gas 140is converted to a plasma 240 by potential between the first and secondpolarity electrodes 185 and 205; and contemporaneously (ii) current flowdefines a least resistive path 245 in the tissue 260; (iii) a portion252 of dielectric structure 122 adjacent current path 245 allowscapacitive coupling to the tissue; (iv) the plasma filament 235 arcsacross a high intensity plasma stream 262 between electrode 185 and theportion 252 of the dielectric structure. In other words, when the aselected voltage potential is reached, the voltage breakdown of the gas140 and capacitively coupling through the dielectric 122 causes a highvoltage current to course through path 245 in the tissue 260. An instantlater, thermal diffusion indicated by arrows 265 causes thermal effectsin a tissue volume 270 a outward from the transient current path 245.The thermal effects in and about path 245 elevates tissue impedance,which thus causes the system to push a conductive path to another randomlocation.

FIG. 9C illustrates the working end components and tissue 260 an instantafter that of FIG. 9B when continued voltage potential causes voltagebreakdown in plasma filament 235′ together with capacitively couplingthrough dielectric 122 to provide another high voltage current to coursethrough path 245′ after which heat diffusion 265′ causes thermal effectsindicated at 270 b. The “scanning” aspect of the ablation method can beunderstood from FIGS. 9A-9B wherein the plasma filaments 235, 235′ andcurrent paths very rapidly jump or scan about the interior chamber 135to thereby deliver current in a path of least resistance 245, 245′ inthe tissue 260.

Now turning to FIG. 9D, another schematic is shown following an intervalof energy delivery in which a multiplicity of current paths through thepre-existing plasma and dielectric 122 have provided thermal effectsdiffused throughout a multiplicity of regions indicated at 270 a-270 f.By this method, it has been found that ablation depths of 3 mm to 6 mmcan be accomplished very rapidly, in for example 30 seconds to 90seconds dependent upon the selected voltage.

In one aspect of the invention, FIG. 10 is a circuit diagramrepresenting the steps of the method of FIGS. 9A-9D which explains thediscovery that return electrode 205 can have a small surface area andnot be subject to significant heating. In FIG. 10, it can be seen thatvoltage potential can increase until a dielectric breakdown occurs inboth the neutral gas 140 and the dielectric structure 122 which cause ahigh voltage current through path P1 to electrode 205, followed by thatpath impeding out, thus causing the current to shift to current path P2,then current path P3 ad infinitum to current path indicated at Pn. Thetissue 260 in FIG. 10 thus is shown as variable resistor in each currentpath as the current path is in continual flux based on the pathincreasing in resistance.

FIGS. 11A and 11B are enlarged schematic illustrations of the method ofusing the embodiment of FIG. 3 to capacitively couple current to tissuewith a gas dielectric 140 in interior chamber 135 (i.e., plasmaindicated at 240). Referring to FIG. 11A, the system is actuated, forexample by a footswitch 208 (FIG. 1) coupled to RF power source 200 andcontrollers 155A and 155B which initiates a gas flow from source 150 toprovide circulating flow through the first (inflow) channel 170,interior chamber 135 and the second (outflow) channel 180. Forconvenience, the embodiments utilizing such a circulating gas flow willbe described herein as using one preferred gas, which is argon. In oneembodiment, the gas flow rate can be in the range of 1 ml/sec to 50ml/sec, more typically from 5 ml/sec to 30 ml/sec. In FIG. 11A, theworking end 120 of the probe is introduced into tissue 260, for exampleto ablate a tumor as in FIGS. 2A-2B. The dielectric structure 122 ispositioned in a desired location to ablate tissue adjacent thereto. Theactuation of the system contemporaneously applies RF energy to electrode185 and the gas flow which instantly converts the non-conductive argon140 to a plasma indicated at 240 in FIG. 11A. The threshold voltage atwhich the argon becomes conductive (i.e., converted in part into aplasma) is dependent upon a number of factors controlled by thecontroller, including the pressure of the argon gas, the volume ofinterior chamber 135, the flow rate of the gas 140, the distance betweenelectrode 185 and interior surfaces of the dielectric surface 122, thedielectric constant of the dielectric structure 122 and the selectedvoltage applied by the RF power source 200. It should be appreciatedthat the actuation of the system can cause gas flows for an interval of0.1 to 5 seconds before the RF generator powers on to insure circulatorygas flows.

FIG. 11A schematically depicts current indicated at 280 beingcapacitively coupled through the wall 132 of the dielectric structure122 to tissue 260, with the electric field lines indicating that highenergy densities do not occur about electrode 205. Rather, as describedabove, the high resistance developed in tissue about the current pathdielectric structure 122 causes rapidly changing current paths and ohmicheating. In one aspect of the invention, the capacitive coupling allowsfor rapid, uniform ablation of tissue adjacent the dielectric structure.FIG. 11B schematically depicts the tissue after the RF energy deliveryis terminated resulting in the ablated tissue indicated at 285.

Now turning to FIG. 12, an alternate working end 120′ is shown in amethod of use. In this embodiment, the dielectric structure 122 issimilar to that of FIG. 3 except the working end 120′ includes a centralsupport member 290 that extends from extension member 214 to a distaltip portion 292. In this embodiment, the central support member 290 cancomprise, or carry, a conductive electrode surface indicated at 295 todelivery energy to the gas 140 in interior chamber 135 for creating theplasma. The embodiment of FIG. 12 also includes concentric gas inflowand outflow channels, 170 and 180, wherein the first (inflow) channel170 comprises a lumen in support member 290 that communicates with aplurality of flow outlets 250 in a distal portion of interior chamber135. The gas outflow port 174 is again disposed in a proximal portion ofinterior chamber 135. The placement of gas inflow and outflow ports inopposing ends of interior chamber allows for effective gas circulationwhich assists in maintaining a predetermined plasma quality. In FIG. 12,the ablative currents and ohmic heating in tissue are indicated at 200.

In another aspect of the invention, FIG. 12 illustrates that at leastone temperature sensor, for example thermocouples 300A and 300B, areprovided within or adjacent to interior chamber 135 to monitor thetemperature of the plasma. The temperature sensors are coupled tocontrollers 155A and 155B to thus allow feedback control of operatingparameters, such a RF power delivered, neutral gas inflow rate, andnegative pressure that assists outflow. By measuring the mass averagetemperature of the media in chamber 135, the degree of ionization of theionized gas 240 can be determined. In one aspect of the invention, themeasured temperature within chamber 135 during operation can providefeedback to gas circulation controller to thereby modulate the flow ofneutral gas to maintain a degree of ionization between 0.01% and 5.0%.In another aspect of the invention, the measured temperature withinchamber 135 during operation can provide feedback to modulate flow ofneutral gas to maintain a temperature of less than 200° C., 180° C.,160° C., 140° C., 120° C., or 100° C. In several embodiments ofpolymeric dielectric structures, it is important to maintain a cold ortechnological plasma to prevent damage to the dielectric. In anotheraspect of invention, the system operating parameters can be modulated tomaintain the mass average temperature within a selected range, forexample a 5° C. range, a 10° C. range or a 20° C. range about a selectedtemperature for the duration of a tissue treatment interval. In anotheraspect of invention, the system operating parameters can be modulated tomaintain a degree of ionization with less than 5% variability, less than10% variability or less than 20% variability from a selected “degree ofionization” target value for a tissue treatment interval. While FIG. 12shows thermocouples within interior chamber 135, another embodiment canposition such temperature sensors at the exterior of the wall 132 of thedielectric structure to monitor the temperature of the wall. It alsoshould be appreciated that multiple electrodes can be provided in theinterior chamber to measure impedance of the gas media to provide anadditional form of feedback signals.

In another embodiment similar to FIG. 12, the working end or flowchannel in communication with the interior chamber 135 can carry atleast one pressure sensor (not shown) and pressure measurement canprovide feedback signals for modulating at least one operationalparameter such as RF power delivered, neutral gas inflow rate, negativepressure that assists outflow, degree of ionization of the plasma, ortemperature of the plasma. In another aspect of invention, the systemoperating parameters can be modulated to maintain a pressure withinchamber 135 less than 5% variability, less than 10% variability or lessthan 20% variability from a selected target pressure over a tissuetreatment interval.

In general, FIG. 13 represents the steps of a method corresponding toone aspect of the invention which comprises containing a non-conductivegas in an interior of an enclosure having a thin dielectric wall,engaging and external surface of the dielectric wall in contact with atarget region of tissue, and applying a radiofrequency voltage acrossthe gas and the dielectric wall wherein the voltage is sufficient toinitiate a plasma in the gas and capacitively couple current in the gasplasma across the dielectric wall and into the engaged tissue. Thismethod includes the use of a first polarity electrode in contact withthe gas in the interior of the thin dielectric wall and a secondpolarity electrode in contact with the patient's tissue.

FIG. 14 represents aspects of a related method corresponding to theinvention which comprises positioning a dielectric structure on a tissuesurface, containing a non-conductive, ionizable gas within thedielectric structure, and applying RF voltage across the gas and tissueto ionize the gas and deliver current through the dielectric structureto the tissue to ohmically heat the tissue.

In general, FIG. 15 represents the steps of a method corresponding toanother aspect of the invention which comprises providing anelectrosurgical working end or applicator with a first gas dielectricand a second non-gas dielectric in a series circuit, engaging thenon-gas dielectric with tissue, and applying sufficient RF voltageacross the circuit to cause dielectric breakdown in the gas dielectricto thereby apply ablative energy to the tissue. The step of applyingablative energy includes capacitively coupling RF current to the tissuethrough the second non-gas dielectric media.

FIG. 16 represents steps of another aspect of the invention whichcomprises positioning a dielectric structure enclosing an interiorchamber in contact with targeted tissue, providing a gas media in theinterior chamber having a degree of ionization of at least 0.01%, andapplying RF current through the gas media to cause capacitive couplingof energy through the dielectric structure to modify the tissue. In thisaspect of the invention, it should be appreciated that an ionized gascan be provided for inflow into chamber 135, for example with a neutralgas converted to the ionized gas media prior to its flow into chamber135. The gas can be ionized in any portion of a gas inflow channelintermediate the gas source 150 and the interior chamber 135 by an RFpower source, a photonic energy source or any other suitableelectromagnetic energy source.

FIG. 17 represents the steps of another method of the invention whichcomprises positioning a dielectric structure enclosing a gas media incontact with targeted tissue, and applying RF current through the gasmedia and dielectric structure to apply energy to tissue, and sensingtemperature and/or impedance of the ionized gas media to providefeedback signals to thereby modulate a system operational parameter,such as RF power delivered, neutral gas inflow rate, and/or negativepressure that assists gas outflows.

Now turning to FIGS. 18A-22, other embodiments of electrosurgicalworking ends are shown that adapted to apply energy to tissue asdescribed above, except that the dielectric structures have differingdielectric portions each having a different relative permittivity tothus cause differential effects (greater or lesser capacitive coupling)in tissue regions in contact with the different portions of thedielectric structure. In one probe embodiment 400 shown in FIGS.18A-18B, a working end carries multiple tissue-penetrating elements 405that are similar to the needle-like working end 120 of FIGS. 1-3. Thetissue-penetrating elements 405 can be extendable from a shaft 410 of anendoscopic instrument 412 by actuation of lever 414. Eachtissue-penetrating elements 405 has a working end with a dielectricstructure 422 as described above and one or more return electrodesindicated at 425. As can be seen in FIG. 19, the tissue-penetratingelements 405 are adapted for penetrating tissue 260, such as a liver, oneither side of a target line 430 that is to be a resection line orplane. Thus, the tissue-penetrating elements 405 can coagulate tissue oneither side of line 430, and thereafter the tissue can be cut andbleeding will be prevented or reduced. Such an instrument 412 can beused in liver resections, lung resections and the like. FIG. 20illustrates a cross-section of the multiple tissue-penetrating elements405 of FIG. 19 in tissue wherein it can be seen that the wall 432 of thedielectric structure varies from a thin-wall portion 435 to a thickerwall portion 436 with each portion extending axially along the length ofthe dielectric structure. As can easily be understood, the thin-wallportion 435 allows a greater coupling of current to adjacent tissue 260when compared to the thicker wall portion 436. For this reason, thedepth of ablated or cauterized tissue regions 440 will vary depending onwhether it is adjacent to thin-wall portion 435 or the thicker wallportion 436. Thus, the instrument can control the depth of ablation byvarying the volume resistivity of the dielectric wall. For example, thethin-wall portion 435 can have a volume resistivity in the range of1.times.10¹⁴ Ohm/cm as described above which can then transition tothicker wall portion 438 having a volume resistivity of 1.5.times.,2.times. or 3.times. triple the 1.times.10¹⁴ Ohm/cm range. As depictedin FIG. 20, the energy delivery converges to ablate or cauterize tissueregions 440 inwardly toward line 430 that is targeted for cutting.Outwardly from line 430 there is less collateral damage due to reducedohmic heating.

FIG. 21 illustrate a plurality of probes 450A-450D that demonstrate asimilar use of “directional” dielectric structures 422 for directionalcontrol of energy delivery to tissue, in this case to provide convergingregions of ablation to ablate tumor 452 as in the working ends of thedevice of FIG. 18A-20. In this embodiment, it can be seen that the probehandles include an indicator mark 455 that indicates the orientation ofthe thin-wall portion 435 or thick wall portion 436 to thus selectivelydirect RF energy delivery. In another embodiment, it should beappreciated that the proximal and distal ends of a dielectric structure422 can be marked with any suitable imageable marker, for exampleradiopaque markings. In another aspect of the invention shown in FIG.20, any probe can carry at least one thermocouple, for examplethermocouples 456 a and 456 b, at locations proximal and distal to thedielectric structure 422 to measure tissue temperatures to provide anendpoint for terminating the delivery of energy. The thermocouplesprovide signal to controllers 155A and 155B to terminate the ablationprocedure. The ablation probes 450A-450D can each carry a returnelectrode as in the working end of FIG. 19, or alternatively there canbe a remote return electrode as indicated at 458 in FIG. 21.

FIG. 22 illustrates another embodiment of electrosurgical working end460 wherein wall 432 of the dielectric structure 422′ varies fromthin-wall portion 435′ to a proximal and distal thicker wall portions436′ with each portion extending radially about the dielectricstructure. As can easily be understood as shown in FIG. 22, the centralthin-wall portion 435′ thus allows a greater coupling of current toadjacent tissue 260 to cause a deeper ablated tissue 440′ as compared tothe thicker wall portions 436′ at the ends of the dielectric structure(cf. ablated tissue in FIG. 11B). In all other respects, the working end460 operates as previously described embodiments.

In the electrosurgical ablation working ends of FIGS. 19-21 above, thedielectric structures 422 and 422′ provide differential or energytransmissibility by means of varying the thickness of a dielectric suchas silicone. A portion of an exemplary dielectric wall 470 with varyingthickness portions 435′ and 436′ is shown in FIG. 23 which representsthe dielectric of FIG. 22. In other words, a varied thickness wall witha uniform dielectric constant or volume resistivity of the material canprovide varied coupling of RF current to tissue about the surface of thedielectric. It should be appreciated that an objective of the inventionis controlled depth of ablation which can be accomplished equally wellby having a uniform thickness dielectric but varying the electricalproperties of the material. FIG. 24 illustrates a constant thicknessdielectric wall 475 with first and second dielectric materials 477 and480 that provides for higher capacitive coupling through material 480.The number of layers of materials, or material portions, and theirdielectric properties can range from two to ten or more. Further,combinations of varying material thickness and dielectric properties canbe utilized to control capacitive coupling of current through thedielectric.

FIGS. 25A-25D illustrate another embodiment of electrosurgical system500 and working end 520 and method of use that is similar to the deviceof FIG. 12 except that the dielectric structure 522 of FIGS. 25A-25D isfabricated of a thin-wall dielectric that can be moved from a firstnon-expanded condition to an expanded condition. In FIG. 25A, theworking end is shown with a distally-extended sheath 524 that can be ofplastic or metal. A first step of a method thus comprises introducingthe working end into tissue interstitially or into a body lumen with thesheath protecting the dielectric structure 522. The dielectric structure522 is then expanded by gas inflows which causes compression ofsurrounding tissue and increases the surface area of the thin dielectricwall in contact with tissue. As can be seen in FIG. 25A, the expandabledielectric 522 can be fabricated of a distensible or non-distensiblematerial, such as a stretchable silicone or a braided, reinforcednon-stretch silicone. The wall thickness of a silicone structure canrange from 0.004″ to 0.030″, and more typically from 0.008″ to 0.015″with an interior volume ranging from less that 5 ml to more than 100 ml.The dielectric structure can have any suitable shape such ascylindrical, axially tapered, or flattened with interior baffles orconstraints. FIG. 26 depicts a cross-section of the sheath 524 and anon-distensible expandable dielectric 522 with a method of folding thethin dielectric wall.

FIG. 25B illustrates multiple subsequent steps of the method whereinsheath 524 is retracted and the physician actuates the gas source 150and controller to expand the expandable dielectric structure 522. Thestructure 522 or balloon can be expanded to any predetermined dimensionor pressure in soft tissue or in any body lumen, cavity, space orpassageway. Radiopaque marks on the dielectric structure (not shown) canbe viewed fluoroscopically to determine its expanded dimension andlocation. The gas circulation controller 155A can circulate gas flowafter a predetermined pressure is achieved and maintained.

FIG. 25C depicts a subsequent step of the method in which the physicianactuates the RF power source 200 and controller 155B to develop highvoltage potential between central support electrode 295 and returnelectrode 205 which, as described previously, can cause a voltagebreakdown in the gas dielectric 140 (FIG. 25B) to create plasma 240 andcontemporaneously capacitively couple current to tissue 260 as indicatedby current flows 530. FIG. 25D depicts the termination of RF energydelivery so that the voltage breakdown and resulting plasma isextinguished—leaving uniform ablated tissue 540 similar to that shown inFIG. 11B.

In one embodiment, the dielectric structure 522 was made from NuSilMED-6640 silicone material commercially available from NuSil TechnologyLLC, 1050 Cindy Lane, Carpinteria, Calif. 93013. The dielectricstructure 522 was fabricated by dipping to provide a length of 6 cm anda uniform wall thickness of 0.008″ thereby providing a relativepermittivity in the range of 3 to 4. The structure ends were bonded to ashaft having a diameter of approximately 4 mm with the expandedstructure having an internal volume of 4.0 cc's. The gas used was argon,supplied in a pressurized cartridge available from Leland Limited, Inc.,Post Office Box 466, South Plainfield, N.J. 07080. The argon wascirculated at a flow rate ranging between 10 ml/sec and 30 ml/sec.Pressure in the dielectric structure was maintained between 14 psia and15 psia with zero or negative differential pressure between gas inflowsource 150 and negative pressure (outflow) source 160. The RF powersource 200 had a frequency of 480 KHz, and electrical power was providedwithin the range of 600 Vrms to about 1200 Vrms and about 0.2 Amps to0.4 Amps and an effective power of 40 W to 80 W.

FIGS. 27 and 28 illustrate another embodiment of electrosurgical system600 that comprises a catheter having working end 610 for treating atrialfibrillation by means of ablation about pulmonary veins PV. Variousmethods of using conventional RF catheters for such treatments areknown. Catheter 610 is configured with a guidewire channel 612 and canbe navigated to a site shown in FIGS. 27-28. The catheter working end620 included an expandable dielectric structure 622 similar to that ofFIGS. 25A-25D that can be expanded to apply pressure between the balloonwall and the tissue to thereafter create a circumferential lesion in apulmonary vein PV. FIG. 28 is a schematic illustration that again showsgas source 150 and gas circulation controller 155A that can expandchamber 635 in the thin-wall dielectric structure 622 to engage the wallof the pulmonary vein PV. In the embodiment of FIG. 28, it can be seenthat the wall of dielectric 622 includes a first (lesser)energy-transmissible region 636 and a second (greater)energy-transmissible region 638 thus allowing a focused circumferentialablation wherein the dielectric has a lesser cross-section as disclosedin co-pending U.S. patent application Ser. No. 12/541,043 (AttorneyDocket No. 027980-000110US) filed on Aug. 13, 2009. Thereafter, the RFpower source 200 and controller 155B can be actuated to convert theneutral gas flow to plasma 240 and contemporaneously ablate tissueindicated at 640. In this embodiment, a first polarity electrode 645 isprovided on the catheter shaft in chamber 635 that can cooperate with asecond polarity electrode on the catheter shaft remote from balloon 622or any other type of ground pad may be used (not shown). In all otherrespects, the method of the invention for ablation of cardiac tissuefollows the steps described above. The balloon can have radiopaquemarkings, and the system can be operated by an algorithm to expand thedielectric structure 622 or balloon to a pre-determined pressure, thendelivery RF energy and terminate delivery automatically. It should beappreciated that additional electrodes can be provided in the balloonsurface (not shown) for mapping conduction in the cardiac tissue.

While FIG. 27-28 illustrate an expandable dielectric 622 for treatingcardiac tissue, it should be appreciate that the scope of the inventionincludes using a similar apparatus and method to controllably applyablative RF energy to any body lumen, vessel, body cavity or space suchas in a stomach, gall bladder, esophagus, intestine, joint capsule,airway, sinus, a blood vessel, an arteriovascular malformation, heart,lung, uterus, vaginal canal, bladder or urethra.

FIGS. 29-31 schematically illustrate another embodiment ofelectrosurgical system 700 and catheter having working end 710 fortreating atrial fibrillation with linear lesions within a heart chamberto block aberrant conduction pathways. Catheter 710 can have a guidewirechannel (not shown) and can be navigated to perform an elongatedablation in a heart chamber as in FIG. 20. In this embodiment, thecatheter working end 720 has a flexible shaft portion 721 that includedan axially-extending thin-wall dielectric 722 in one surface forengaging tissue to provide a linear lesion as depicted in FIG. 31. Thecatheter shaft 721 is deflectable by means of a pull-wire 728 that canbe actuated from a catheter handle. FIG. 30 is another schematicillustration that shows the gas source 150 and gas circulationcontroller 155A that can provide gas circulation within interior chamber735 interior of the thin-wall dielectric 722. The RF power source 200 iscoupled to a lead 738 and elongated first polarity electrode 740 in theinterior chamber 735. The RF power source 200 and controller 155B can beactuated to convert the neutral gas flow to a plasma andcontemporaneously ablate tissue engaged by dielectric 722 as describedabove. The second polarity electrode can be provided on the cathetershaft remote from dielectric 722 or any type of ground pad may be used(not shown). In all other respects, the method of the invention forablation of cardiac tissue follows the steps described above. Theworking end can have radiopaque markings, and the system can be operatedin accordance with algorithms. It should be appreciated that additionalelectrodes can be provided in the catheter working end (not shown) formapping conduction in the heart pre- and post ablation.

FIG. 32 illustrates another catheter working end 720′ that is similar tothat of FIGS. 29-31 that is deflectable by a pull-wire 738 to provideall or part of circumferential lesion in a pulmonary vein (see FIGS.28-29). In this embodiment, the thin-wall dielectric 722′ extends aroundthe exterior surface of the articulated working end.

FIGS. 33 and 34 illustrate another embodiment of electrosurgical system800 that comprises a catheter having working end 810 for treating anesophagus 811, for example to ablate Barrett's esophagus, to applyenergy to lower esophageal sphincter or for other disorders. The systemoperates as previously described in FIGS. 25A-28 in embodiments thathave an expandable dielectric structure. In the dielectric structure 822of FIGS. 33-34, the expansion of the structure is provided by a skeletalsupport member such as an interior spring-like member, with an optionalpull-cable actuation mechanism. As can be seen in FIG. 34, a helicalsupport member 825 is provided that is capable of a contractedcross-section (axially-stretched) or an expanded cross-section inchamber 835 which is assisted by pulling central cable 828 in cathetershaft 830. In this embodiment, the dielectric can again comprise athin-wall silicone as described above. In this embodiment, it has beenfound that the support member 825 can be of a conductive metal andcoupled to RF power source to function as a first polarity electrode840. The second polarity electrode (not shown) can be located elsewhereon the catheter is a location in contact with tissue, or a ground padcan be used.

FIG. 35 illustrates another embodiment of electrosurgical system 800′that is similar to that of FIG. 34 with a dielectric structure 822 thatis supported in an expanded condition by a plurality of bowed-outskeletal support members 825′ that are assisted by pull-cable 828. Inthis embodiment, the portion of the pull-cable within chamber 835functions as a first polarity electrode 840′. In operation in any of theembodiments above, it has been found that the first polarity electrodecan provide sufficient voltage to create a substantially uniform plasmain an interior chamber (see FIGS. 2, 8, 11A, 28, 30, 33, 35) of anon-expandable or expandable dielectric when the surface of theelectrode is less than 15 mm, less than 10 mm or less than 5 mm from theinterior wall of the dielectric. This maximum dimension from thedielectric wall to the electrode 840′ is indicated at gap G in FIG. 35.In has also been found that, in operation, the first polarity electrodecan provide voltage to create a substantially uniform plasma in aninterior chamber of a non-expandable or expandable dielectric wall whenthe electrode contacts the surface of the dielectric 822 as in FIG. 34,but the electrode surface should engage less than about 10% of theinterior surface of the dielectric wall. If the first polarity electrodeengages greater than about 10% of the interior surface of the dielectricwall, then the “flux” of energy delivery through tissue as schematicallydepicted in FIG. 8 will be reduced, a greater capacitive coupling mayoccur about the regions of the electrode(s) in contact with the wallwhich can reduce the uniformity of tissue ablation.

FIG. 36 illustrates another embodiment of electrosurgical system 900wherein the working end 910 comprises first and second opposable jaws912A and 912B that are adapted for clamping tissue for coagulation,sealing or welding tissue 914. In one embodiment, both jaws have atissue-engaging surface that comprises a dielectric structure 922A, 922Bthat is similar in function to all other such dielectric structuresdescribed above. FIG. 36 is a schematic illustration that again showsgas source 150 and gas circulation controller 155A that can deliver gasto chambers 935A, 935B in the jaws. The RF power source 200 andcontroller 155B can be actuated to convert the neutral gas flows in thechambers 935A, 935B into plasma 240 and contemporaneously to applyenergy to engaged tissue 914. In this embodiment, the jaws carry firstand second polarity electrodes 945A and 945B, respectively, to thus makejaw function by means of a contained ionized gas and capacitivecoupling, which differs from previous embodiments. It should beappreciated that one jaw can comprise a single electrode surface, asopposed to the plasma-initiated capacitive coupling system of FIG. 36.The dielectric structures of FIG. 36 are of the type described in FIGS.4B and 5A wherein the thin-wall dielectric material is supported bysupport columns, posts, channels of the like.

FIGS. 37 and 38 illustrate another embodiment of electrosurgical system1000 again includes a catheter or probe shaft 1002 extending to aworking end 1010 that carries an expandable dielectric structure 1022.In this embodiment, the dielectric structure 1022 includes a pluralityof interior chambers, for example first and second chambers 1024A and1024B. The expansion of the dielectric structure 1022 can be provided byskeletal support members such as interior spring-like members asdescribed above or by expansion by fluid pressure of gas inflows or acombination thereof. Each chamber is configured to carry a flexibleinterior electrode, with adjacent chambers having opposing polarityinterior electrodes, such as electrodes 1040A and 1040B indicated at (+)and (−) polarities in FIGS. 37 and 38, to allow another form a bi-polarablation. In this embodiment, the electrodes and support members cancomprise the same members. As can be seen in FIG. 37, the external wallof dielectric structure 1022 has thin wall portions 1032A and 1032B forcapacitively coupling energy to tissue, and a thicker wall portion 1042that insulates and separates the first and second chambers 1024A and1024B. The flexible electrodes 1040A and 1040B are operatively coupledto RF power source 200. The gas inflow source 150 and negative pressuresource 160 are coupled to in inflow and outflow channels communicatingwith each interior chamber, 1024A and 1024B, independently. In thetransverse sectional view of FIG. 31, the open terminations 1046 and1048 of the inflow and outflow channels can be seen in each interiorchamber, 1024A and 1024B. Thus, each chamber is provided with acirculating gas flow (indicated by arrows in FIG. 37) similar to thatdescribed in previous embodiments with respect to single chamber workingends.

FIG. 38 is a schematic sectional view of the dielectric structure 1022deployed in a targeted tissue 1050. It can be understood that the systemcan be actuated to circulate gas in chambers 1024A and 1024B which thenis converted to a plasma 240 in each chamber as described previously. Inthis embodiment and method of use, the capacitive coupling occursthrough the thin dielectric walls 1032A and 1032B in paths of currentflow indicated at 280 in FIG. 38. Whereas the previous embodimentsillustrated a single chamber containing a plasma that capacitivelycoupled current to a non-gas electrode, the embodiment of FIGS. 37 and38 depicts the use of at least two contained plasma electrodes andcapacitive coupling therebetween. It should be appreciated that thenumber of adjacent chambers carrying opposing polarity electrodes can beutilized in a thin-wall dielectric structure, for example 2 to 10 ormore, with the chambers having any suitable dimensions or orientationsrelative to one another.

In another aspect of the invention, depicted schematically in FIGS.39-41B, the electrosurgical system and working end 1200 and methodsinclude generating and controlling the plasma filaments or streamers1210 as depicted in FIGS. 8 to 9C. Such plasma streamers dischargeelectrical potential and can be described functionally as a dielectricbarrier discharge. Such plasma streamers are generated through adielectric barrier that couples RF current from an electrode to thedielectric and allowing for momentary lines of electrostatic flux in athin-wall dielectric to deliver current across the dielectric to tissue.As used herein, the term dielectric barrier discharge describes aspecific type of high-voltage, alternating current, gaseous dischargethat can be created in an atmospheric or near-atmospheric pressurerange. This near-atmospheric pressure gas can be provided in an enclosedspace with a circulating gas flow as described in embodiments above.

FIG. 39 schematically illustrates one embodiment of electrosurgicalworking end 1200 with a dielectric structure 1240 comprising a thin-wallstructure or construct 1244 enclosing an interior chamber 1245. Thethin-wall construct 1244 is a dielectric such as silicone or an othermaterial as described above with a support frame (see FIG. 34) or othersupports (see FIG. 4A) that are not shown for convenience. The thin-wallconstruct also can comprise a rigid material such as a glass or ceramic.A first polarity electrode 1250 is within interior chamber 1245 and asecond polarity electrode 1255 is exterior of the chamber 1245 and inone embodiment is mounted on a portion of the dielectric wall 1244. Thesecond polarity electrode 1255 can be mounted on a thin insulativesubstrate 1258 so that electrode 1255 is not in direct contact with thedielectric wall 1244. The interior chamber 1245 again is configured forgas flows therethrough during operation as described in previousembodiments.

FIG. 39 depicts a first surface 1262 of the dielectric wall 1244 ordielectric barrier that contacts tissue 1260. The second surface 1264 ofthe dielectric wall interfaces with the neutral gas 1265 in the interiorchamber 1245. FIG. 39 further depicts discharges in the form of plasmafilaments or plasma streamers 1210 that occur between the surface ofelectrode 1250 and the second surface 1264 of the dielectric wall 1244.

FIGS. 40A and 40B are enlarged schematic views of a portion of thedielectric wall 1244 of FIG. 32 that illustrate how the plasma streamers1210 can be generated to limit or control the spatiotemporal chaos ofsuch streamers. The low charge mobility of the dielectric wall 1244makes it impossible for charges generated in the gas 1265 to immediatelycross the dielectric to conduct to the electrode 1255 positioned at theexterior of the interior chamber 1245 (see FIG. 29). Referring to FIGS.40A-40B, with each half-cycle of the driving oscillation, the voltageapplied across the gas can exceed that required for breakdown thusresulting in the formation of narrow discharges or plasma streamers 1210that initiate the conduction of electrons toward the more positiveelectrode. As charge accumulates on the dielectric layer at the end ofeach plasma streamer PS, the voltage drop across the plasma streamerdiminishes and falls below a discharge-sustaining level and thedischarge is thus extinguished. The low charge mobility on thedielectric 1244 results in the self-arresting aspect of such plasmastreamers and also limits the lateral region over which the gap voltageis diminished. At certain selected voltages, a discharge depositscharges on the dielectric surfaces, which sets up an electric field thatopposes the applied field resulting in an abruptly lowered field in alocalized region of the dielectric wall 1244 (see FIGS. 40A-40B). Whenvoltage is reversed, the field is reinforced by the charge depositedduring the preceding half-cycle—which can result in the next dischargeto occur in the location of a previous streamer resulting in spatialcontrol of such plasma streamers 1210. This aspect of dielectric barrierdischarges in the form of such plasma streamers permits neighboring,somewhat parallel, plasma streamers to be created. Further, the plasmastreamers form in close proximity to one another and can form asubstantially stable spatiotemporal pattern. It should be appreciatedthat the electrode 1250 can be parallel or non-parallel relative to thedielectric wall 1244 and such plasma streamer patterns and spacing canbe substantially stable when coupling energy to a tissue volume havinguniform electrical parameters.

In another aspect of the invention relating to the energy-deliverysurface of FIGS. 40A-40B, the arrangement of electrode 1250, enclosedgas volume 1265 and dielectric wall 1244 allows dielectric-barrierdischarges to be utilized to thereby create and momentarily concentrateelectrostatic lines of flux in the thin-wall dielectric to allow RFcurrent to cross the dielectric to the tissue. FIGS. 41A-41E are furtherenlarged schematic views of the wall dielectric 1244 at different stagesof interaction with a pattern of plasma streamers 1210 that are spacedapart by streamer spacing SS (FIG. 41E). FIG. 41A shows the dielectricwall 1244 at rest. FIGS. 41B-41D depict an initial interval that mayrange from nanoseconds to milliseconds or more after initiation ofenergy delivery in which the applied voltage causes chaotic plasmastreamers 1210 to form. After an initial energy delivery interval, theplasma streamers can settle into a substantially stable pattern withstreamer spacing SS as depicted in FIG. 41E. In order for the dischargesto occur, the local regions of the dielectric structure are subjected tomomentary concentrations of electrostatic lines of flux 1275 or electronpermeability as depicted in FIGS. 41B-41E. The RF current thus iscapable of coupling across the concentrations of electrostatic lines offlux 1275 in the dielectric wall 1244.

At some applied voltages, there is complete spatiotemporal chaos amongthe dielectric barrier discharges. By experimentation, it has been foundthat control of several system parameters can reduce the spatiotemporaldisorder or chaos of the discharges, and control of certain parameterscan substantially eliminate such spatiotemporal chaos and createspatially repetitive locations of plasma streamers 1210 and repetitivespacing between streamers when applying energy to tissue. Chart A belowlists the several system parameters and ranges thereof that enable theenergy delivery methods of the invention.

TABLE-US-00001 CHART A Actual Min-Max Dielectric constant 3.0-3.51-10,000 (Relative static permittivity) Gap (G) between 0-0.5 mm 0-5 mminterior chamber electrode and inner surface of dielectric wall Surfacearea of 5-17.5 cm² 0.1-30 cm² dielectric (Energy-delivery surface)Dielectric wall 0.005″-0.010″ 0.001″-0.020″ thickness Gas flow(replacement 0.5-1 slpm 0.1-2 slpm volume/time) Frequency of 480 kHz 100kHz-20 MHz alternating current Gas pressure 760 Torr 10 Torr-1000 TorrField strength 0.3 MV/m-8 MV/m 50,000 V/m-1600 MV/m

In one aspect of the invention, a method of applying energy to tissuecomprises contacting tissue with an energy-delivery surface and creatingsubstantially stable patterns of plasma streamers adjacent a dielectricbarrier that couple RF current to, and across, the energy-deliverysurface to the engaged tissue. The pattern of plasma streamers iscreated in a gas-filled chamber that is at least partly bounded by thedielectric energy-delivery surface.

In another aspect of the invention, a method of reducing orsubstantially eliminating spatiotemporal chaos of plasma streamerscomprises providing and controlling a plurality of system parameterslisted in Chart A, consisting of (i) controlling the dielectric constantof the dielectric wall, (ii) controlling the “gap” or spacing G betweenelectrode 1250 in plasma reaction chamber 1245 and dielectric wall 1244(FIG. 39), (iii) controlling the surface area of dielectric wall intissue contact, (iv) controlling the thickness of the dielectric wall,(v) controlling the circulation of neutral gas through the interiorchamber, (vii) controlling the frequency of the current, (viii)controlling the pressure in the interior chamber, and (ix) controllingthe field strength which relates to voltage and spacing betweenelectrode 1250 and dielectric wall 1244.

FIG. 42 illustrates an enlarged schematic view of working end 1200 ofFIG. 39 wherein the energy-delivery structure or construct 1240comprises a thin dielectric wall 1244 enclosing interior chamber 1245and electrode 1250 in which plasma streamers 1210 can be created toapply energy to tissue 1260 in the manner as schematically depictedpreviously in FIGS. 41A-41E. In the greatly enlarged view of FIG. 42, itcan be seen that a first energy-delivery surface 1262 of dielectric wall1244 contacts tissue 1260 and transitory plasma streamers 1210 cross thespace between the surface of electrode 1250 to a second (inner) surface1264 of the dielectric wall 1244. FIG. 42 illustrates schematically thata number of plasma streamers 1210 over a time interval are spaced apartby spacing SS if the electrical parameters of tissue 1260 remainsubstantially uniform during a treatment interval. FIG. 42 also showsschematically that discrete local regions or focal points 1280 of thedielectric wall 1244 are briefly modified as the plasma streamers 1210and current paths 1285 in the tissue cause the electron-permeability ofsuch focal points 1280 of wall 1244. The system and method thus causespatiotemporal switching of the focal points 1280 of energy applicationabout the dielectric surface by coupling energy to said points withtransitory plasma streamers 1210, which are self-arresting so that thehigh temperature, high-intensity plasma does not measurably damage ordegrade the dielectric wall.

In the embodiment schematically depicted in FIG. 42, the tissue regions1288 that are indicated with hatching represent regions that areaffected by Joule heating about the current paths 1285. This Jouleheating of tissue is similar to that depicted in FIGS. 9A-9D above. Inone working end embodiment 1200 as depicted in FIG. 42, it has beenfound that controlling the parameters in Chart A above can provideplasma streamers 1210 and current paths 1285 that cause transitoryelectron-permeability in the dielectric wall 1244 and which limitheating of focal points 1280 of the dielectric wall 1244. The embodimentof FIG. 42 schematically illustrates a system that optimizes andmaximizes Joule heating of the engaged tissue. In this embodiment, atleast the dielectric constant of wall 1244, the wall thickness, gapdimension G, gas flow and electric field strength in the plasmastreamers are selected within ranges to provide an electrical impedanceacross the gap G that is less than the impedance of the contacted tissue1260, or less than twice the impedance of the contacted tissue or lessthan three times the impedance of the contacted tissue 1260. In a systemembodiment having such characteristics, the effects in tissue will besubstantially caused by Joule heating of tissue--and not conductiveheating from the surface of the dielectric wall 1244. In other words,greater Joule heating, and lesser conductive heating, will be providedwhen the impedance across the plasma in gap G is less than the impedanceacross the tissue 1260. In general, a lower impedance plasma can beprovided by lower gap G dimensions, high dielectric constants of thedielectric wall and high field strengths.

FIG. 43 illustrates an enlarged schematic view of the working end 810 ofFIG. 34 wherein the energy-delivery construct 1240 comprises athin-wall, distensible dielectric material 1244 supported by frame 1290.The interior chamber 1245 is configured with a central electrode member1250 and neutral gas flows are provided through the central electrodemember 1250 as described above in the text accompanying FIG. 34. In theembodiment of FIG. 43, the plasma streamers 1210 again are formedbetween the electrode 1250 and second surface 1264 of dielectric wall1244 in the same general manner as in the embodiment of FIG. 42. In onesystem embodiment, referring to FIG. 43, it has been found that theparameters in Chart A can be adjusted within the indicated ranges toprovide plasma streamers 1210 that maximize heating of the focal points1280 while at the same minimizing Joule heating of tissue along thecurrent paths 1285 in tissue 1260. The embodiment of FIG. 43 thus usesthe dielectric wall 1244 as a heat applicator in which the heated focalpoints 1280 passively conduct heat to tissue adjacent each focal point,which indicated as conductively heated region 1295 of the tissue. Inthis aspect of the invention, it has been found that a high plasmaresistance, compared to the tissue resistance, can result in streamers1210 coupling energy to the focal points 1280 of the wall 1244 withoutcoupling as much energy through the electron-permeable regions to causeJoule heating of the tissue. In this aspect of the invention, utilizinga dielectric wall 1244 with a lower dielectric constant will provide forgreater passive tissue heating from the heated material of focal points1280 and lesser Joule heating along current paths 1285 in tissue.Further, a system embodiment that has a greater dimension gap G, ingeneral, will be conducive to greater passive tissue heating from theheated dielectric wall 1244 lesser Joule heating in adjacent tissue. Inone embodiment configured for conductive heating of tissue from a heatedenergy-delivery surface can have a dielectric wall 1244 with anelectrical permittivity ranging from about 1 to 20, a gap G ranging fromabout 1 mm to 10 mm, and other parameters within the ranges indicated inChart A.

Another aspect of the invention can be seen schematically in comparingFIGS. 42 and 43, wherein the plasma streamers 1210 have somewhatdifferent characteristics when the discharge is across a lowerresistance plasma (and higher dielectric constant wall 1244) rather thana higher resistance plasma. In a lower resistance plasma, the plasmastreamers 1210 are focused with fewer branching filaments at theinterface (second surface) 1264 of the dielectric wall 1244, asindicated schematically in FIG. 42. In a higher resistance plasma, theplasma streamers 1210 are more branched and irregular and interface withthe second surface 1264 of the dielectric wall 1244 more broadly, asindicated schematically in FIG. 43. Experimentation has shown thathigher resistance plasmas as depicted in FIG. 43 are suited for heatingthe dielectric wall to create a heat applicator surface for passiveheating of adjacent tissue. In the embodiment of FIG. 43, the focalpoints 1280 that are heated by the plasma streamers are believed tolarger in a high resistance plasma, while such streamers 1210 stillremain spaced apart in repetitive locations as described above. In oneembodiment configured for maximizing Joule heating of tissue, thedielectric wall 1244 has an electrical permittivity ranging from about20 to 10,000, a gap G that is less than about 5 mm, and other parameterswithin the ranges indicated in Chart A.

In another aspect of the invention, the plasma streamers 1210 can becreated with a duty cycle in which voltage is applied to initiate theplasma in on/off intervals wherein each “on” interval is at least longenough to create a discharge across gap G which can be greater than 1millisecond, 100 milliseconds or 500 milliseconds. In such a duty cycle,the “off” intervals can be at least 1 millisecond, 100 milliseconds or500 milliseconds. In one system embodiment, the duty cycle canconfigured to cooperate with the thermal relaxation time of dielectricmaterial of the thin-wall enclosure that interfaces with the plasmastreamers. For example, referring to FIG. 43, if the plasma streamers1210 heat the focal points to about 200° C. in a voltage “on” interval,and the dielectric material relaxes in temperature back to 50° C. in0.25 seconds, then the duty cycle can have “off” intervals ofapproximately 0.25 seconds to insure that the dielectric wall does notoverheat which can extend the life of the dielectric structure.

In general, referring to FIGS. 39-43, the system of the invention forapplying energy to tissue comprises a probe having an energy-deliverysurface configured for spatiotemporal switching of focal points ofenergy application 1280 about the surface in contact with tissue, agas-filled chamber 1245 interior of the energy-delivery surface and avoltage source configured for creating transitory plasma streamers 1210in the gas to thereby provide spatial and temporal switching of energycoupling to the focal points. FIG. 44 illustrates the steps of a methodof the invention comprising contacting tissue with a thin-wallenergy-delivery construct, and causing spatiotemporal switching of focalpoints of energy application about the construct by coupling energy tosaid focal points with transitory plasma streamers, which therebydistributes energy application over the area of the contacted tissue tocause uniform tissue ablation. The energy-delivery surface comprises athin wall dielectric material. The system includes a first electrode1250 within the interior chamber 1245 and coupled to the voltage source.Further, the system includes a second electrode carried on the shaft ofthe probe or proximate to, but electrically insulated from, theenergy-delivery surface 1262. As described above, the system alsoincludes a gas source configured for providing a flow of a neutral gasthrough the interior chamber 1245.

In another aspect of the invention, a method comprises causing thespatiotemporal switching of plasma streamers between first and secondelectrodes positioned respectively at an interior and exterior ofdielectric wall 1244 and a surface 1262 in contact with tissue. Further,the temporal aspect of the switching step occurs within less thanmilliseconds. Also, the spatial aspect of the switching step moves thefocal points 1280 apart from one another a minimum distance. The methodof energy delivery can be utilized in an interstitial application or theenergy-delivery surface can be deployed in a body lumen, space orcavity.

Another aspect of a method of the invention is shown in FIG. 45 whichcomprises contacting tissue with a wall 1244 having an energy-deliverysurface 1262, coupling energy through the wall by providingelectron-permeable focal points 1280 wherein the transitory plasmastreamers 1210 and current paths 1285 in tissue result in Joule heatingof tissue about the current paths 1285. Another method invention isshown in FIG. 46 which comprises contacting tissue with a wall 1244having energy-delivery surface 1262 and coupling energy to focal points1280 within the surface by transitory plasma streamers 1210 therebyheating the focal points 1280 and thereafter causing conductive heatingof tissue adjacent the focal points.

In another aspect of the invention, as can be understood from FIGS.42-43, the material of wall 1244, the thickness of the wall 1244, itsdielectric constant, the gap G and other parameters can be selected toprovide a desired ratio of passive conductive heating of tissue versusJoule-heating of tissue.

Although particular embodiments of the present invention have beendescribed above in detail, it will be understood that this descriptionis merely for purposes of illustration and the above description of theinvention is not exhaustive. Specific features of the invention areshown in some drawings and not in others, and this is for convenienceonly and any feature may be combined with another in accordance with theinvention. A number of variations and alternatives will be apparent toone having ordinary skills in the art. Such alternatives and variationsare intended to be included within the scope of the claims. Particularfeatures that are presented in dependent claims can be combined and fallwithin the scope of the invention. The invention also encompassesembodiments as if dependent claims were alternatively written in amultiple dependent claim format with reference to other independentclaims.

What is claimed is:
 1. A system for applying energy to tissuecomprising: a probe having an energy-delivery structure configured forspatiotemporal switching of focal points of energy application about thesurface in contact with tissue; a gas-filled chamber interior of theenergy-delivery surface; and a voltage source configured for creatingtransitory plasma streamers in the gas to thereby provide spatial andtemporal switching of energy coupling to the focal points.
 2. The systemof claim 1, further comprising a first electrode within the chamber andcoupled to the voltage source.
 3. The system of claim 1, furthercomprising a second electrode carried on the probe or proximate theenergy-delivery surface.
 4. The system of claim 1, further comprising agas source configured for providing a flow of gas through the chamber.5. The system of claim 1, wherein the energy-delivery surface comprisesa dielectric.
 6. The system of claim 5, wherein the energy-deliverysurface comprises a silicone.
 7. The system of claim 5, wherein theenergy-delivery surface comprises a non-distensible material.
 8. Thesystem of claim 5, wherein the energy-delivery surface comprises adistensible material.
 9. The system of claim 5, wherein theenergy-delivery surface is expandable from a compacted configuration toan expanded configuration.
 10. The system of claim 1, further comprisinga controller configured for adjusting an electrical parameter inresponse to the degree of distension of a distensible energy-deliverysurface.
 11. A method of electrosurgical energy delivery comprisingcreating dielectric-barrier discharges to couple RF current from anelectrode to targeted tissue.
 12. The method of claim 11, wherein thedischarges are high-voltage, alternating current, gaseous discharges.13. The method of claim 11, wherein the discharges are gaseousdischarges in a near-atmospheric pressure range gas.
 14. The method ofclaim 11, wherein the discharges are gaseous discharges between theelectrode and a dielectric barrier in contact with the tissue.
 15. Themethod of claim 12, wherein the dielectric barrier comprises a thindielectric wall surrounding an interior chamber, the gaseous dischargesare within the interior chamber and an exterior of the wall contactstissue.
 16. The method of claim 12, wherein the voltage of thehigh-voltage discharges is selected to reduce spatiotemporal chaos ofthe discharges.
 17. The method of claim 12, wherein the voltage of thehigh-voltage discharges is selected to eliminate spatiotemporal chaos ofthe discharges.
 18. The method of claim 12, wherein the voltage is aleast 100V.
 19. The method of claim 15, wherein the gaseous dischargesare within a noble gas or mixture of noble gases in the interiorchamber.
 20. A method of applying electrosurgical energy to tissuecomprising: engaging tissue with energy delivery surface; and creating asubstantially stable, large-scale pattern of plasma filaments thatcouple RF current to, and across, the energy deliver surface to theengaged tissue.
 21. The method of claim 20, wherein the pattern of theplasma filaments are created in an interior chamber at least partlybounded by the energy delivery surface.
 22. The method of claim 20,wherein the energy delivery surface is a dielectric.
 23. The method ofclaim 20, wherein the pattern of plasma filaments are created between alength of an electrode and adjacent length of the energy deliverysurface.
 24. The method of claim 20, wherein the pattern of plasmafilaments are created in a noble gas between an electrode and the energydelivery surface.